This invention relates to printing presses in general and, in particular, to a web-fed rotary printing press capable of producing multiple-page signatures or sections each including two or more "center spreads," by which term is meant the sheets of paper or other printable material each bearing a pair of facing pages, irrespective of the presence or absence of columnar division between the pages, of the matter printed thereon, or of the positions of these sheets relative to the other sheets of the signature.
The rotary printing press has been known and used extensively in which a plurality of webs from separate stocks or rolls are concurrently printed upon, superposed one on top of another, fed through a device that gives them their down-the-middle fold, and cut into individual sheets. There are thus obtained signatures each consisting of a predetermined number of pages in consecutive order. Produced in this familiar manner, however, each signature has only one center spread, only one paper bearing two center facing pages in the inmost position of the folded signature.
Attempts have been made in recent years at production of signatures each having two or more center spreads. Japanese Unexamined Patent Publication No. 10-29387 represents one conventional approach to this objective, teaching a web-fed rotary printing press designed explicitly for production of multiple-center-spread newspapers. This prior art apparatus comprises a slitter for cutting the web along its centerline into a pair of web halves, a first triangular shaped former for folding a first web half down the middle, a second similar former for similarly folding a second web half, and guide means for directing the folded first web half, which is to form additional center-spreads, between the desired pages of the multiple-page sections formed from the second web halves.
To dwell a bit more on this prior art apparatus, the two formers are oriented in the same direction along the paths of the web halves just downstream of the slitter. Consequently, the first web half, which is to form folded additional center spreads, lies, on being folded by the first former, in a plane that is displaced 90 degrees from that of the second web half traveling toward the second former; that is, the first web half is then at 90 degrees out of phase with the second. An angled guide bar (turning bar) and guide rollers are therefore provided between the two formers in order to correct the 90-degree phase displacement of the first web half, bringing the same back into phase with the second web half and further aligning the fold of the first web half with the centerline of the second web half. Then, with the first web half superposed on the second, both web halves are guided to the second former. The thus folded web halves are subsequently cut and folded transversely, into signatures including the additional center spreads.
It is stated in the specification of the noted unexamined patent publication that another additional former may be provided to insert another additional center spread into each signature. It is also said that the production of multiple-center-spread signatures of very large numbers of pages is possible by adding angle guide bars and associated rollers.
An objection to this prior art contrivance concerns in particular the angled guide bar between the two formers. Since these formers are oriented in the same direction, the interposition of the angled guide bar between the formers is a requisite to return the first web half, which has been turned 90 degrees in phase on being folded by the first former, back into phase with the second web half before they come to the second former. Essentially in the form of a fixed rod, the guide bar has introduced considerable friction to the web half. The consequences of such friction have been especially inconvenient because the web half has been previously doubled up. The two folds of the web half have been very easy to slip longitudinally one over the other, resulting in wrinkling, as well as transversely, resulting in both wrinkling and deviating of the web half away from the predetermined path. In either case the production of the press has suffered immensely in quality.
Another known approach to multiple-center-spread signatures is found in the article entitled, "Development of Double Center Spread Systems, " in the 1997-1 issue, No. 159 Pages 78-81, of Newspaper Technology published by Japan Newspaper Association on Mar. 25, 1997. The article suggests the provision of two formers in vertically spaced positions for folding two webs in the folding section of a rotary printing press. Between the two formers are, here again, an angled guide bar, a set of rollers for guiding the web from the upper former to the bar, and another set of rollers for guiding the web from the bar to the lower former.
The upper former longitudinally folds a web that is to provide an additional center spread. The angled guide bar turns the folded web 90 degrees in phase, into a face-to-face relationship with the other webs which have been printed by other printing units but which are not yet folded. The additional center-spread web, folded and turned 90 degrees, is inserted between the unfolded other webs, with the fold of the folded web in register with the centerlines of the unfolded webs. The superposed webs subsequently travel past the lower former, by which only the unfolded webs are folded. The webs, now all folded, are then cut and folded transversely into signatures of a predetermined number of pages, in which there are at least two center spreads.
This second prior art system is also said to permit adaptations for greater numbers of center spreads in each signature, by providing an additional former or formers and additional angled guide bar or bars, together with an additional web or webs to provide an additional center spread or spreads. After being printed, folded, and turned 90 degrees in phase, such additional web or webs are to be inserted between on the other printed webs before the latter are folded at its own former.
Just like the first recited prior art device, this second one has the angled guide bar together with the associated rollers for turning the first web 90 degrees as it travels between the two formers which are oriented in the same direction. Traveling in frictional engagement with the angled bar, the web has been just as likely to give rise to the noted inconveniences as in the first prior art device. An additional drawback is that, disposed in the narrowly confined space between the two formers, the guide bar and rollers have been very difficult of maintenance.
Both guide bar and guide rollers can be dispensed with, and the difficulties arising therefrom overcome, if the two formers are oriented with an angular difference of 90 degrees therebetween, as indeed disclosed in Japanese Unexamined Utility Model Publication No. 58-87748. However, this conventional device merely teaches to fold a web twice longitudinally by guiding it through the successive formers. It discloses no means whatsoever for guiding one folded web into superposition with other, unfolded webs before feeding these webs to the other former. This known device should not therefore be taken as anticipatory of the instant invention, it being totally unapplicable to the creation of multiple-center-spread signatures.